A major design consideration for enzymes active in the detoxication of foreign compounds, appears to be a broad specificity for primarily lipophilic molecules. The glutathione transferases are a good example in that they catalyze any reaction in which glutathione serves as a nucleophile if the second substrate is bound to the protein; act as binding and storage proteins intracellularly for bilirubin among thousands of other ligands; and form irreversible covalent complexes with very reactive electrophiles including carcinogens. Thiol S-methyltransferase, recently obtained in homogeneous form, is another example of a detoxicating enzyme active in transferring a methyl group to lipophilic mercaptans. A similar situation obtains with phenol and sterol sulfotransferases, enzymes which are now also available as homogeneous proteins.